Method of welding aluminum and other metals



3, 1962 M. F. REJDAK &020,610

METHOD OF WELDING ALUMINUM AND OTHER METALS Original Filed Dec. 20, 1955 A TTOENEY &ZMO Patented Feb. 13, 1962 disclosed a method of welding copper rail bonds to steel rails utilizing highly heated molten copper produced by an exothermic reaction of the thermit type, and such method has now been in successful commercial use for a number of years on a large scale. Patents 2,277,0l4 to Noble G. Carlson and 2,654,129 to Edward B. Neff disclose certain preferred forms of cast welding apparatus adapted to be employed with the metal producing exothermic reaction mixture, and in application Serial No. 42.2,032 of Donald J. Burke for "Welding Apparatus, filed April 9, 1954, there is disclosed another form of apparatus particularly adapted for the joining together of two opposed cable ends by means of a cast weld connection. I

For a great many years, copper wire and cable has been accepted as the standard conductor for electric current although certain other metals such as aluminum and silver have been utilized in special applications where their qualities are particularly desirable. In recent years, however, the use of aluminum wre and cable has very greatly increased, and it often becomes necessary to join aluminum cables together or to connect the same to copper bus bars, for example. The molten metal produced by the exothermic reaction m'xture disclosed in the aforesaid Cadwell Patent 2,229,04S has not proved satisfactory for the welding aluminum articles, and more especially for cast welding aluminum conductors such as cable to other cable, bus bars, grounds, etc., such improved process and material providing a cast weld metal having improved hot strength and wetting ability.

Another object is to provide such process and material which will aflord a cast weld juncture in which the formation of cracks on cooling is substantially eliminated.

Still another object is to provide such method of welding which is not hindered by the usual oxide film found on articles of aluminum.

A further object is to provide such material and method of welding utilizing an exothermic reaction mixture to produce the molten weld metal in situ at the proper temperature and under properly controlled conditions.

A still further object is to provide a cast welded connection wherein the weld metal is interfused with the aluminum article or articles.

Other objects of the invcntion will appear as the description proceeds.

To the accomplishment of the foregoing and related ends, said invention then comprises the features herein after fully described and particularly pointed out in the claims, the following description and the annexed drawing 2 setting forth in detal certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

Said annexed drawing is a semi-diagrammatic crosssection through a graphite crucible and associated mold cavity adapted to receive two opposed cable ends to be cast welded together.

Referring now more particularly to such drawing, the welding apparatus may comprise two graphite blocks such as 1 hollowed out to provide an upper crucible portion 2 and mold cavity portion 3, the two halves being temporarily clamped together as shown and described in Burke application Serial No. 422,032, for example. Two dry and clean cable end portions 4 and 5 are clamped in the mold cavity with their opposed ends located substantially vertically below sprue 6 which is closed by means of a small metal disc 7, ordinarily steel. The exothermic reaction mxture which may be supplied in the form of a Cartridge is empted into the crucible so that the principal metal forming materials 8 fill the lower portion of the crucible and the starting powder 9 forms a layer on top. Such starting powder may then be ignited with a flint gun, and it in turn ignites the exothermc reactior mixture to produce the molten metal charge which melts through disc 7 and drops into mold cavity 3, surrounding the cable end portions and bonding thereto. The mold may then be opened and the welded connection removed. V

As previously indicated, it has proven extremely dif ficult to obtain a satisfactory weld where aluminum articles are concerned, as for example when attempting to weld aluminum cable to a copper bus bar. Not only does the aluminum conduct away heat with great rapidity, but also the thin film of aluminum oxide normally covering its surface is highly refractory in character and mlitates against the obtaining of a true weld in which the metal of the aluminum article is intimately interfused with 'the weld metal. I have found that a satsfactory weld, and' more particularly a weld of good physical strength and electrical conductivity, may `be obtained by the employment of molten tin or tin alloy as the weld metal which is so highly heated that it is effective to melt a portion of the'aluminum (including aluminum alloy) article while covering such melted portion and preventing contact with the atmosphere. The thin refractory aluminum oxide film is thus locally flushed away and true interfusion of the underlying aluminum with the weld metal is obtained.

I have further discovered that such weld met-al may desrably be produced by an exothermic reaetion between stannic or stannous oxide and suificient aluminum to re-` duce such oxide, sufiicient additional metal being present in the reaction mixture to control the violence of the reaction and to form an alloy with the tin metal produced thereby of proper strength, malleability and electrical conductivity.

I have also discovered that certain selected fluxng agents when incorporated in the exothermc reaction mixture greatly facilitate proper carrying out of the operation.

Ordinarly, not only is aluminum the preferred reducing agent for the tin oxide, but also an excess of aluminurn metal should be included in the reaction mixture to regulate the reaction and alloy with the molten tin produced thereby. I have further found that by inclusion of copper in the exothermic reaction mixture either as copper metal or in the form of oxide to be reduced by a portion of the aluminum, an improved alloy is produced having much increased hot strength and wetting ability as well as forming a cast weld juncture with a greatly reduced tendency to form cracks on cooling. The copper may be added in the form of metallc copper aluminum alloy.

The basic reaction using stamic oxide, cuprous oxide and aluminum may be written as follows:

3SnO 3Cu O +=6Al- 3Sn 6Cu 3Al a preferred formulation may be stated by parts by Weight:

37 parts SnO +8 parts Cu O+10 parts Al- 29 parts Sn+7 parts Cu Using stannous oxide, cuprous oxide, and aluminum, the reaction may be written:

3SnO+3Cu O -|-4Al- 3Sn+ 6Cu+2.-\l O or stated by parts by weight: 32 parts S11O+8 parts Cu O+ parts Al- 28 parts Sn+7 parts Cu A similar basic reaction occurs when cupric oxide is used with either stannous or stannic oxides. With stannic oxide:

3Sn0 +3CuO+6Al-3Sn+3Cu+3A1 O 37 parts SnO +4 parts CuO+ parts Al- 29 parts Sn+3 paris Cu With stannous oxide:

3S11O+3CuO+4Al- 3Sn+3Cu+2Al O 32 parts Sn0+4 parts CuO+5 parts Al- 28 parts Sn+3 parts Cu The metallic tin produced by any of the foregoing reactions is extremely highly heated, but the reaction unless regulated as described below is so violent and spatters the reaction mixture so exceedingly that it is not practical. I accordingly moderate the reaction by incorporating in the reaction mixture an excess of from 8 to 40 parts of aluminum powder based on the parts formulas given above. An excess of 30 parts alurninum` powder yields the best results. If the copper is added to the exothermic reaction mixture as metallic copper powder or alloyed with `all or a portion of the aluminum, the quantity of excess aluminum required to moderate the reaction may be somewhat reduced. Preferably the particle size of the various Components of the mixture should range between 200 and 325 mesh.

From about 2% to about 25% copper should be present in the resultant cast weld metal, With 9% copper being preferred. The excess alumrun in the reaction mixture not only serves to moderate, regulate and control the otherwise too violent exotherrnc reaction, but also alloys with the molten metallic tin produced, together with the molten copper, to form, a highly heated molten alloy capable when dropped into the mold cavity of interfus'ng with the aluminum cable end portions to form a strong malleable cast weld. The temperature of such molten charge will preferably be in excess of 2,000 F. and the cast weld metal is aecordingly enabled actually to melt portions of the cable and wash away the refractory oxde film thereon to form an integral weld. The aluminurn cable or other aluminum article may also be cast welded by my new process to articles of brass, bronze, and nichrome. In these cases, both the aluminum article and the other article are interfused with the cast weld metal. Copper, steel, stainless steel and cast iron articles may also be bonded to aluminum articles in accordance with my invention if properly prepared, as by dipping in molten tin, so that the cast weld metal will braze thereto.

By far the preferred uxing agent which may be included in the exothermic reaction powder mixture is calcium fluoride. If desired, a proportion of cryolite or sodiumchlorde may be included therewith.

The following examples of suitable exothermic reaction powder formulations for welding aluminum in accordance with my invention are given by way of illustration only and are not to be considered as limitng the invention.

Example 1 Percent Tin oxide 46.8 Aluminum powder 42.2 Cuprous oxide 7.3 Calcun fiuoride 3.7

Example 2 Tin oxide 45.2 Aluminum powder 41.8 Cuprous oxide 9.5 Calcium fluoride 3.5

Example 3 y Tin oxide 52.4 Aluminum powder 36.1 Copper powder 7.5 Calcium fluoride 4.0

Example 4 Tin oxide 52.4 Aluminnm powder 28.6 /50 Cu-Al alloy 15.0 Cal cium fluor-ide 4.0

Example 5 Tin oxide 49.1 Aluminun powder 43.3 Cuprous oxide 3.8 Calcium fluoride 3.8

Example 6 Tin oxide 43.4 Aluminum powder 39.3 Cuprous oxide 13.8 Calcium fluoride 3.5

Example 7 Tin oxde 40.4 Aluminum powder 36.5 Cuprous ox'de 19.8 Calcium fiuorde 3.3

The ranges of ingredients permissible in the usual formulation `are indicated below, it being understood that there must always be suficient aluminum to reduce the oxides present:

Percent Tin oxide from 51.1 to` 35.4 Aluminum powder from 43.3 to 36.5 Cuprous oXide from 1.8 to 24.8 Calcium fluo'ide from 3.8 to 3.3

As prevously indicated, certain other metals may be included in the exothermic reaction mixture for the purpose of regulating the same instead of the excess aluminum provided in the examples given above. In general, an amount of aluminum powder will be included slightly more than the theoretical amount required to reduce the tin oxide present (and also the copper oxide, if present) and then approximately 20% by weight of nickel, tin, silver, iron, or chromium may be included instead of the excess aluminum. Illustrative examples of exothermic reacton mixture formulations in accordance with my invention in which a metal other than aluminum is utilized to control the reaction and to alloy with the molten tin and copper are given below:

Example 8 Percent Tin oxide I I 54.8 Aluminum powder 14.4 Silver 19.3 Cuprous oxide 7.1 Calcium fluoride 4.4

I Example 9 Tin oxide 55.8' Aluminum powder 14.3 Nickel 18.2 Cuprous oxide 7.1 Calcium fluorde 4.6

V Example 10 Tin oxid 55.8 Aluminum powder 14.6 Iron 16.6' Cuprous oxide r i 7.1 Calcium flnoride y `5.9

Example -11 Tin oxide y i 53.9 Aluminum powder 14.1 Tin 20.4' Cuprous oxide I t 7.1 Calcium fluoride 4.5

Example 12 Tin oxide I 56.9 Alu-minum powder i 14.4 Chromium 17.6 Cuprous oxide 7.1 Calcium fluor- 4.0

Stannic oxide is commercially available in p article sizes i able 'particle size for the aluminum powder and other' metals present in the reaction rnxture is approximately 325 mesh. It will be appreciated that the excess metals employed for the purpose of regulating the reaction may include one or more of the several metals indicated above i as suitable for this purpose. The principal requirement is that' they shall not be volatilized by the heat of the reaction and will alloy with the molten tin to form a strong malleable cast weld of good electrical conductivity.

A suitable ignition powder formulation is as follows:

. Percent Fine (red) copper oxide 36.11 Black copper oxid V 30.56 Fine aluminum alloy (60% Ou, 40% Al) 16.667 Fine aluminum powder 8.33 Red phosphorus 8.33

Various other suitable igniton miXtures are well known in the art. They may themselves be ignited in various' ways, the safest and most satisfactory being through use i 3500 F. The most suitable alloying metals listed above have boiling points as follows:

Aluminum has a melting point of 1220 F. and tin has a melting point of 449 F. The alloys produced by reaction of the exothernic reaction mixtures listed above all have melting points below 20`O0 F.

It will be seen from the foregoing that I have provided a novel exothermic reaction mixture which permits me to weld an aluminum article to another metal article by igniting such exothermic reaction mixture to produce highly heated molten copper alloy of tin having a temperature in excess of 2000 F., such molten meta-l immediately being delivered to a mold cavity defined in part by such articles to be joined, the hcat content of such molten charge'causing a portion of the aluminum article to interfuse therewith to form a strong malleable connection. r In certain cases, the heat of such molten charge may be as high as 3000 F.

' Stannous oxide, while also suitable for use in the reaction, is too expensive for ordinary commercial use. molten metal produced by my exothermic reaction will ordinarily and preferably comprise a major proportion of tin by weight. Where the term tin oxide is used heroin, stannicoxideis intended, and percentages and parts given are by weight.

' It is usually desirable, and when welding aluminum cable and the like it may be quite important, to apply a suitable fiux to the parts to be Welded capable of dis solving the aluminum oxide coating when heated. A good practice is first to degrease the articles With an ap propriate solvent and then swab a concentrated water solution thereon having the following composition:

This coating is ,dried completely prioto performance of the welding operation, leaving a flux incrustation on the articles. Other suitable fluxes for my purpose include:

. Parts by weight Lithium chloride 20 Sodium chlorid 10 Potassium chlorde 10 Zinc chlorid 10 Water Lithium chlorid 9 Lithium fluoride 5 Sodium chloride 30 Potassium chlor 'd 40 Zinc chlor 10 Water 50 The u'se of fluxes when welding aluminum is, of course, well known in the art.

This application is a division of my co-pending application Serial No. 554,234, filed December 20, 1955, now Patent No. 2,821,760.

Other modes of applying the principle of the invens tion may be employed, change being, made as regards the details described, provided the features stated in any' of the following claims or the equivalent of such be employed.

The r I therefore particularly point out and distinctly claim` as my nventionr num, controlling the violence of the reaction by inclusion of excess aluminum in the exothermc reaction mixture such excess aluminum alloying with the molten tin andcopper produced, such molten tin being much in eX- cess of such molten copper, immediately delivering such alloy having a major proportion oftin'by weight and' I a temperature above 2,000 F., and contacting such article e 1. The method of welding an 'aluminum article to another 'metal artcle which c'omprises 'exother nically reducng tn oxde and cuprous oxide with metallic alumiresultant molten 'alloy of tin, copper, and aluminum at r a temperature' of at least 2,000 F. to 'a mold cavity defined in part by such articles to be welded, the heat content of' such molten charge being sufi'icient partially to melt such aluminum article for interfusion therewith to form a strong malleable' cast weld connectionof good electrical conductivty. V

2. The method ofi claim'l', Wherein the other 'metal action, alloying a substantial but minor amountof copper therewth,'the balance being essehtially' tin, and contacting such aticle with such molten alloy at a temperature r in excess of'2,000 F. sufficient to melt the opposed sur'- face' of such article, such oxide coating inthe region of' 'contact beng disspated and such` alloy and aluminum g aninterfused cast weld; i i i r r 4. The method of welding to an aluminumarticle havr ing an ialurninum `oxi'decoating thereon comprising proe ducng a highly heated molten tinecopper alloy containing from 2% to copper by weight, the balance being essentially tin, and Contacting such article with such molten alloy at a temperature in excess' of 2,000 F. sufiicient r to melt the .opposed surfaceof such article, such oxide coating in the region of contact 'beings disspated and` 'such tin' and aluminum formng an interfused cast weld.

`5. The method of welding to an aluminum article having an aluminum oxde coating thereon comprising producing highly heated molten tin by an exothermic reaction, alloying copper and aluminum therewith to form a molten alloy having a temperature above 2,000 F., the tin comprising a large portion of such molten alloy, and Contacting such article with such hot molten alloy to melt the opposed surface of such article, such oxde coating in the region of contact being dissipated and such molten alloy and aluminum article forming an interfused cast weld.

6. The method of welding to an aluminum article having an aluminum oxde coating thereon comprising producing highly heated molten tin by an exothermic reaction, alloying copper and silver therewith to form a molten alloy having a major proportion of tin by weight and a temperature above 2,000 F., and contacting such article with such hot molten alloy' to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten alloy and aluminum article forming an interfused cast weld.

7. The method of welding to an aluminum article having an aluminum oxide coating thereon comprising producing highly heated molten tin by an exotherrnic reaction, alloyng copper and nickel therewith to form a molten alloy having a major proportion of tin by weight and a temperature above 2,000 F., and Contacting such article with such hot molten alloy to melt the opposed surface of such article, such oxide coating in the region of contact being dissipated and such molten alloy and aluminum article forming an interfused cast Weld.

8. The method of welding to an aluminum article having an aluminum oxide coating thereon comprising producing highly heated molten tin by an exothermc reaction, alloying copper and iron therewith to form a molten With such hot molten alloy to meltthe opposed surface 'ofsuch article,'such oxide coating ,in the region ,of contact being dissipated and such molten alloy and aluminum article' forming an interfused cast Weld. y

9. The method of welding to an aluminum article having an aluminum oxidecoatng thereon comprising producing highly heated molten tin by an exothcrmic reaction,' alloying copper and ehrornium therewith to form a molten' alloy having a major proporton of tin by 'weight and a temperature above 2,000 F., and contacting 'such article With such hot molten alloy' to mett the` .opposed 'surface of such article, such oxide coating in' the region of contact bengdissipated ,and such molten alloy and aluminum article forming an interfusedcast weld.

r `'10.' Themethod of weldingto analuminum article having an aluninumoxide coating thereon comprising producing highly heated moltentin by an exothermic rev r action, alloying copper andtin therewith to form amolten alloy having a major proportion of tin by weightand a temperature above 2,000 F.,'and Contacting such article v r with such'hot molten alloyto :nelt the opposed surface of such article, such oxide coating in the region of contact being dissipated andsuch molten alloy' and` alurninum article formingan interfused cast weltl.` r 11.'The method: of welding to= an aluminum article having an aluminum oxide' coating thereon ;comprising` producingboth highly heated molten tin and highly heated molten copper by anexothermic'reaction, alloying a `metal therewith `effective to lower the temperature of r the molten tin-copper alloyand produce an alloy there:

'With of good'strength malleability and electrical conductivity when hardened, such alloy comprising a major' proportion of tin by weight and in its molten state as i r thu's produced having 'a temperature of, at least 2,000 i F., Contacting `such article withsuch molten' alloy, to

r melt the opposed surface of such article, such .oxide coati i ing in the 'region' of 'contact being, dssipated andsuch moltenalloy and aluminum article'forning an'intcrfused cast weld.

'12. The method of welding to an aluminum article having an aluminum oxide coatng thereon comprising producing highly heated molten tin by an exothermic reaction, alloying a substantial but minor amount of copper therewith and Contacting such article with such molten alloy at a temperature in excess of 2,000 F. sufiicient to melt the opposed surface of such article, such oxde coating in the region of contact being dissipated and such alloy and aluminum forming an interfused cast weld, such article having a salt flux applied thereto to facilitate such dissipation of such oxide coating.

13. The method of welding an aluminum article to another metal article selected from the class consisting of copper, steel, stainless steel and cast iron which comprises exothermically reducing tin oxide and cuprous oxide with metallic aluminum, controlling the violence of the reaction by inclusion of excess aluminum in the exothermic 'eaction mixture, such excess aluminum alloying with the molten tin and copper produced, such molten tin being much in excessrof such molten copper, immediately deliveringsuch resultant molten alloy of tin, copper, and aluminum at a temperature of at least 2,000 F. to a mold cavity defined in part by such articles to be welded, the heat content of such molten charge being sufficient partially to rnelt such aluminum article for interfusion therewith to form a strong brazed connection of good electrical conductivity.

References Cited in the file of this patent UNITED STATES PATENTS 587,?:03 Ellis Aug. 3, 1897 (Other refet-emes on following page) 1,637,o33 2,151,302 2,229,o45 2,280,s73 2,535,397

UNITED STATES PATENTS Basch July 26, 1927 Scheller Mar. 21, 1939 Cadwell Jan. 21, 1941 Udy Apr. 28, 1942 5 Duch et al. Dec. 26, 1950 

1. THE METHOD OF WELDING AN ALUMINUM ARTICLE TO ANOTHER METAL ARTICLE WHICH COMPRISES EXOTHERMICALLY RE- 